Demonstrationsprojekt Berlin-Margaretenhöhe: Dezentrale Klärtechnik vor Ort erprobt und auf Wirtschaftlichkeit geprüft.

In Berlin, drinking water is exclusively abstracted from groundwater. For this reason, well monitoring is important to ensure a good water quality and a high well capacity. The project WellMa, which stands for well management, aims at the optimization of the operation and maintenance of drinking water abstraction wells. During the first work package of the preparatory project phase WellMa1, available data of 615 wells in Berlin were evaluated. Since ochre formations appear most frequently, the context between iron-related clogging and hydrochemistry, well construction and operation was examined. Based on the statistical analysis, TV camera inspections were identified to be the most reliable marker to indicate the iron-related clogging status of a well. The results were classified into four stages and set into relation to relevant chemical, operational and constructional parameters to determine trends and correlations. Outliers lie below or above the detected trends, as given by the generated boxplots. Seven parameters have to be taken into account: iron, manganese and nitrate-nitrogen concentrations, top of the first filter, distance to the next surface water, mean discharge rate and monthly operation hours. Wells, whose outlier parameter based on one of the following criteria, were excluded from further investigations: (i) clogging state 1, which should be lower according to the outlier parameter, at a high remaining specific capacity, (ii) nitrate-nitrogen values that should lead to higher clogging degrees lying slightly out of the range given by the boxplot, (iii) classification of the clogging degree shortly after construction, regeneration or H2O2 treatment and (iv) missing information about clogging state in the BWB well files and missing TV inspection videos to verify deviating values. The analysis demonstrates a complex interaction between the single parameters. High nutrient inflow because of river bank filtration, leakages of the casing, high discharge rates or unconfined conditions superimpose the distance to the surface of a deep screened well. Since the encrustations are mediated by bacteria, the composition and permeability of the biofilm varies depending on the engaged microorganism. Furthermore, the thickness and dimension are influenced by the available time for bacterial growth, the inflow velocity, number of switchings or position of the water levels.

Die Überwachung von Brunnen läuft nach Monitoringprogrammen, in denen der Ablauf der erforderlichen Maßnahmen geplant ist. Heutzutage werden zunehmend die Betriebsparameter kontinuierlich ermittelt und durch Fernübertragungssysteme zu zentralen Datenbanken übertragen. Basierend auf einem solchen System hat die Firma Veolia in Frankreich ein Software-Modul entwickelt, welches die Messdaten der Wasserstände, der gepumpten Wassservolumen und der Schaltungen der Pumpen in einer Datenbank ausliest und Bilanztabellen und Diagramme in Excel erstellt. Dies bildet die so genannten „Bilans Lerne“, die es ermöglichen, die Entwicklung der Brunnen kontinuierlich zu überwachen. Die Anwendung dieses Instruments an den Brunnen der Berliner Wasserbetriebe (BWB) wurde drei Monate lang beispielhaft an fünf Brunnen am Standort TegelHohenzollernkanal getestet. Ziel war es, zu prüfen, inwieweit sich die gegenseitigen Beeinflussungen zwischen den Brunnen und die für Berlin spezifischen Betriebspläne auf die Datenauswertung und Berechnungen des Moduls auswirken. Dazu sollte auch untersucht werden, ob das vorgegebene Messintervall, die Instabilitätskoeffizienten und die minimale Dauer für die Ermittlung der Betriebs- und Ruhewasserstände auf Berlin übertragen werden können oder ob Optimierungen notwendig sind. Dazu wurden zunächst einmal die gegenseitigen Beeinflussungen der Brunnen aufeinander geschätzt: Die Reichweiten der Absenkungstrichter erreichen mindestens 90 m und die betrachteten Brunnen sind ca. 50 m voneinander entfernt, so dass die Schaltungen eines Brunnens sich immer auf den Wasserstand in den unmittelbar benachbarten Brunnen auswirken. Dies ist auch auf den Gangliniendiagrammen der gemessenen Wasserstände deutlich zu sehen. In den dreimonatigen Messungen konnten die „Bilans Lerne“ für die fünf ausgewählten Berliner Brunnen erstellt werden. Allerdings sind die Ergebnisse der Modulanwendung teilweise unvollständig. Dies liegt vor allem daran, dass die Berliner Brunnen im Vergleich zu Brunnen in Frankreich sehr selten geschaltet werden, das Modul jedoch, um alle Parameter wie geplant ermitteln zu können, auf den Wechsel von Pump- und Auffüllungsphasen zurückgreift, um Fördermengen, Absenkungsbeträge und spezifische Ergiebigkeiten zu berechnen. So kann unter den Berliner Betriebsverhältnissen lediglich ein Wert der spezifischen Ergiebigkeit pro Monat berechnet werden, während für die französischen Brunnen i. d. R. ein Wert pro Tag berechnet wird. Da dies im Vergleich zum derzeitigen Stand der Praxis eine Verbesserung hinsichtlich der Häufigkeit der Ergiebigkeitsmessungen darstellt, kann die Benutzung eines solchen Instrumentes in Berlin empfohlen werden. Damit das Instrument in Berlin lückenlose Berechnungen durchführen kann, sind jedoch Anpassungen und Optimierungsschritte für die Makros erforderlich. Darüber hinaus könnte z. B. als eine Anpassung an die Betriebsbedingungen spezifisch für Berlin erwogen werden, die Messungen weniger häufig durchzuführen.

The overall project WellMa, which stands for well management, aims at the optimization of the operation and maintenance of drinking water abstraction wells. For this purpose, in addition to a statistical analyses of well data (report D 1.2) and first field investigations to compare various diagnosis methods (report D 1.3), a review of literature during the preparatory phase WellMa1 should answer the following questions: (1) Which processes affecting the well performance and conditions can occur? (2) Which correlation exists between well ageing and well characteristics? (3) How can such well ageing be recognized at an early stage? (4) What is the state of the practice to restore a good performance and condition? (5) What can be done during well design and construction to prevent well ageing? (6) How can well operation be adjusted to slow-down well ageing processes? Based on textbooks, standards and professional articles published in large number since the middle of the nineties, the state of the art was gathered and compared to current practice at BWB and Veolia to identify possibilities for improvement and specify the need for further investigations to be proposed for WellMa2. 1) Three well ageing types involving different processes could be identified. These are chemical, biological and physical clogging. They are closely linked to the characteristics of the exploited aquifer, such as the physical properties of the formation or the chemical composition of the groundwater. 2) The evaluation of these site-specific aquifer characteristics, the impacts from well design and the observed effects on the well performance and condition and their development with time of operation should be used to specify the individual ageing potential for each well site. 3) The early recognition of well ageing implies the need to monitor wells (1) regularly and (2) with comparable methods. As suitable indicators, the development of water levels and discharge rates to calculate the specific drawdown and specific capacity, the pump surveillance and the visible condition of the well interior could be identified. 4) Both, the assessment of the ageing potential and the monitoring of a reference value describing the state of the well lead to the specification of maintenance requirements. Generally, three strategies could be identified, ranging from sheer operation, over reactive maintenance to regular condition assessment and preventive treatment. Concerning the choice of maintenance method, key criteria must always be the well design, its state of construction, the well ageing type and location. Up to now, patterns linking well characteristics and the success of maintenance could not be identified. Thus, maintenance relies on practical experience and the willingness to discuss limitations and disadvantages of methods as open as the advantages on side of the rehabilitation companies. 5) For well design and construction, the technical standards were summarized, describing the necessary steps for proper dimensioning, drilling, choice of materials and final well development. Not only the avoidance of nonconformities and the careful evaluation of the advantages, but also the restrictions of different well design alternatives, e.g. for the accessibility of rehabilitation, assure an optimal well ageing prevention and well operation. 6) Furthermore, well operation could be identified as a key element and critical factor codetermining the lifetime, but at the same time the economic efficiency of a well. It is always a compromise between demand, technical possibilities and economic considerations, for which reason general standards or technical guidance are not available so far. They need to be developed individually considering present well ageing processes and the quantification of impacts. Comparing the state of the art with current practice at BWB and Veolia, room for improvement could primarily be identified for monitoring and subsequent data processing for both, operational parameters (to assess well performance and condition), and maintenance (to evaluate the success of applied treatments). Based on the recommendations derived on this state of the art review, within WellMa2 the effects of measures for preventing and treating well ageing shall be quantified so that the benefits can be assessed for future optimized well management.

The study aims at validating the point-of-use investigations on long-term gravity-driven ultrafiltration for a scaled-up system, which could produce drinking water for a community of 100-200 inhabitants using natural surface water. Eawag, KWB and Opalium conceived a membrane-based small-scale system (SSS) which can operate without crossflow, backflush, aeration or chemical cleaning. Equipped with a biosand filter as pretreatment, it is designed to be robust, energy-sufficient (gravity-driven) and run with restricted chemical intervention (only residual chlorine). The containerised unit (10’) requires to be fed with raw water at a 2 m-height (energy-equivalent to ~8Wh/m3). As sole operational requirement, the membrane reactor is simply to be drained (i.e. emptied) on daily to weekly basis to superficially remove the material retained by the membrane and accumulated in the module. Otherwise, the system, which is only driven by a 40 cm differential pressure head (i.e. 40 mbar), is totally self-determined and autonomous. This report details the validation tests performed at Veolia Water Research Center in Annet-sur-Marne (France) from January to August 2009 : the gravity-driven UF compact unit showed promising results in regards to flux stabilization and flow capacity. Although early investigations take place in winter, an initial flux stabilization to 2.5 lmh is observed, which is below the reference results from the Eawag lab tests (i.e. 7-10 lmh, at 20 ± 2°C). However, the “scaled-up” system can benefit from a weekly drainage which seems to enhance the flux to 4-5 lmh, and thereby, the unit is to produce more than 4 m3/d, which is consistent with the design target of 5 m3/d. Moreover, the increase of the drainage frequency (to 3 times/week) along with warmer temperatures – leading to a better membrane permeability and biological activity - contribute to a further enhancement to 5-7 lmh. This is particularly relevant for South Africa, for which decentralized water supply is a burning issue and where the unit is to be further tested from November 2009. The investigations also highlighted the critical performance of the biosand filter as pretreatment. More than the UF step – whose membrane integrity was confirmed with bacterial analyses, the pretreatment step needed more frequent (i.e. monthly) O&M requirements. Therefore, the pretreatment necessity will be further assessed in South Africa where high turbidity peaks could represent an extra challenge for the unit.

In ländlichen Gegenden stellen Kleinkläranlagen eine kostengünstige Lösung für die Abwasserentsorgung dar. Nach der in Europa gültigen Definition von Kleinkläranlagen handelt es sich hierbei um Anlagen zur Behandlung von häuslichem Abwasser bis zu 50 EW. In Deutschland sind ca. 2,2 Millionen Kleinkläranlagen in Betrieb bzw. werden installiert. In Frankreich werden etwa 10 bis 12 Millionen Einwohner von dezentralen Systemen versorgt mit steigender Tendenz. Die technischen Lösungen solcher Systeme reichen von Pflanzenkläranlagen über Schilfrohrfilter bis zu Belebungsanlagen. Alle auf dem europäischen Markt verfügbaren Systeme müssen der EU-Zertifizierung EN 12566-3 entsprechen, die einen indeststandard bezüglich Betriebssicherheit und Reinigungsleistung setzt. Weiterhin müssen, je nach nationalen oder regionalen Vorgaben, zusätzliche Richtlinien beachtet werden. Es sind nur wenige Informationen verfügbar über Effizienz, Betriebszuverlässigkeit und Wartungsfreundlichkeit im realen Betrieb der unterschiedlichen am Markt verfügbaren Kleinkläranlagentypen, was aber gerade für Kunden, aber auch für Anbieter von Abwasserdienstleistungen von besonderem Interesse ist. Um diese Lücke zu schließen, wurden in vorliegender Studie über eine Dauer von 14 Monaten nebeneinander 12 unterschiedliche Systeme unter realen Betriebsbedingungen verglichen und bewertet. Die Studie liefert damit detaillierte Informationen zu den Leistungsmerkmalen unterschiedlicher Anlagentypen hinsichtlich Reinigungsleistung, Ablaufwerte, Betriebsaufwand, Schlammbehandlung und Energieverbrauch. Die Untersuchungen erfolgten an einer Auswahl von auf dem Testfeld des Bildungs- und Demonstrationszentrum für dezentrale Abwasserbehandlung e.V. (BDZ) in Leipzig zu Demonstrations-und Schulungszwecken vorinstallierten Kleinkläranlagen sowie zwei zusätzlich dort eigens für das Vorhaben eingebauten Systemen.

Riverbank filtration (RBF) denotes the process whereby river water is induced to infiltrate into a groundwater system by well operation adjacent to banks. In Central Europe, RBF has been common practice for 100 years to produce drinking water. Due to the easy implementation and little maintenance necessary, BF has been suggested to be a useful drinking water treatment for developing and newly-industrialised countries. Experience from Europe has demonstrated that RBF is suitable to remove a range of organic and inorganic contaminants while an exhaustion of cleaning capacity has not been observed. RBF systems can mitigate shock loads and are particularly known for the efficient removal of pathogens, suspended solids and algal toxins from surface water, all being water quality parameters of high relevance in developing and newly-industrialised countries. Another benefit of RBF operation is the storage capacity which may help to balance freshwater availability in areas experiencing high variations of precipitation and run-off. This report aims at evaluating the relevance and opportunities of RBF systems to provide safe water to these countries. In order to evaluate the relevance and opportunities of RBF systems to developing and newly-industrialised countries, the report is structured to address key considerations and (i) identify prerequisites for successful RBF operation based on the experience in Central Europe and the United States, (ii) assess the removal potential of RBF for various water contaminants based on available literature, the TECHNEAU investigations in India and NASRI data from Berlin and (iii) evaluate the sustainability and relevance of RBF operation with regard to the particular needs in developing and newly-industrialised countries.

Work package WP 5.2 “Combination of Managed Aquifer Recharge (MAR) and adjusted conventional treatment processes for an Integrated Water Resources Management“ within the European Project TECHNEAU (“Technology enabled universal access to safe water”) investigates bank filtration (BF) + post-treatment as a MAR technique to provide sustainable and safe drinking water supply to developing and newly industrialised countries. One of the tasks of WP 5.2 is to develop a Decision Support System (DSS) as a first qualitative tool to assess the feasibility of bank filtration for drinking water supply in developing countries. The Bank Filtration Simulator (BFS), which is the subject of this report, is a sub-model used within the DSS to compute steady-state solutions for a two dimensional groundwater flow field in the horizontal plane for BF settings. Input parameters are required for aquifer, bank and well characteristics to calculate the BF share analytically. In addition the minimum travel time between bank and well is computed numerically. The sensitivity analysis yielded that the analytical calculated BF share is the most reliable output parameter, since its value is grid-independent. The most sensitive input parameters for the BF share calculation are the hydraulic conductivity of the aquifer and the clogging parameter, which both are the most uncertain ones to estimate. The accuracy of the numerically computed minimum traveltime of the BFS was cross-checked against a MODFLOW model, which produced only a very small discrepancy below 5%. Due to the lacking time-dependency of the BFS model its application is only appropriate on a management horizon for which the system’s boundary conditions (e.g. baseflow, clogging parameter and pumping rates) do not change significantly over time. In a nutshell it is therefore highly recommended to use the BFS only as a qualitative assessment tool in a first planning step to evaluate the feasibility of BF systems. Nevertheless the qualitative outputs give a valuable physically based insight of the system’s behaviour for distinct operational scenarios (e.g. minimal/maximum pumping rates) in order to add transparency and reproducibility to the decision making process.

While climate change is an emerging hazard to water supply, literature on the vulnerability of bank filtration (BF), a proven technique of drinking water production in Central Europe and North America, is yet scarce. The Intergovernmental Panel of Climate Change (2007) has projected a global temperature increase between 1.1 and 6.4 °C by 2100. This will affect vital factors for water supply such as precipitation regime, groundwater recharge, run-off, river discharge and raw water quality. Projections on climate change and the implications are difficult because of the uncertainties associated with climate scenarios and modelling. However, in Europe and North America where BF is in operation, the projected increase in seasonal floods and droughts has already been experienced. In addition, site-specific considerations (e.g. land use, demographic trends) are to be taken into account to evaluate the potential impacts on water supply. To fill the current gap in literature, this report provides a first overview on how changing environmental conditions may affect BF operation.